Under the Treaty of Versailles, the highly industrialized Saar Basin, including the Saar Coal District (German: Saarrevier), was to be occupied and governed by the United Kingdom and France under a League of Nations mandate for a period of fifteen years. Its coalfields were also to be ceded to France. During this time, the Saar Territory was governed by the five-person Governing Commission[4] (German: Regierungskommission; Reko) made up of representatives of the occupation forces. Under the terms of the mandate, the Commission had to include at least one French person and one German resident of the Saar.[5] After that time, a plebiscite would be implemented to determine the Saar's future status.

There was no home-rule by the citizens in the Saar Territory but the Governing Commission decided on all legislation autonomously.[6] According to paragraph 23 of the Versailles Treaty the Governing Commission had to establish an assembly of elected representatives of the inhabitants of the Saar Territory in such a manner as the Governing Commission would determine itself.[4][6] So on 24 March 1922, after four years without any official representation of the people, the Reko decreed the formation of a Saar Territory assembly called the Regional Council (German: Landesrat).[7] In June 1922 the Governing Commission held the first election of the Regional Council, and starting with the second election of the Regional Council the legislation period was extended from three to four years, with elections in 1928, and in 1932.

The Regional Council counted 30 members, the Governing Commission (Reko) deliberately determined one person as the chairperson, the president of the Regional Council (Landesratspräsident).[8] In the first legislation period the Reko did not even chose the president from the midst of the Regional Council.[8] The assembly was no parliament, but only to be consulted, the representatives were only to be heard, but had no say in in the agenda to be debated, let alone in legislation.[8] The agenda of matters to be debated was exclusively set up by the Governing Commission.[8] The members of the Regional Council had neither the right of interpellation, nor the right to actively bring a subject to the agenda, let alone they were entitled to table a bill.[8] Its members did not enjoy immunity.[8] So in case the Governing Commission did not set an issue on the Regional Council's agenda it could only send delegations to the League of Nations with pleads, and so the Regional Council did.[8]

With this situation being as it was all the representatives elected to the Regional Council, regardless of the party, opposed the system of autocratic rule in the Saar Territory. All parties demanded the return of the Saar Territory to Germany where the people could elect the parliament, and the latter again, the government in self-determination. Only after the Nazi takeover in Germany, outlawing all other parties except of their own NSDAP, the Bezirk Saar of the SPD and the Saar branch of the KPD left the opposing block, advertising to uphold the status quo. For the 1935 status referendum Social Democrats and Communists suggested the voters to decide in favour of a continued status quo, without prevailing.

In 1933, a considerable number of political opponents of National Socialism moved to the Saar, as it was the only part of Germany that remained under foreign occupation following World War I. As a result, anti-Nazi groups agitated for the Saarland to remain under British and French occupation under a League of Nations mandate. However, as most of the region's population was German, the mandate was unpopular. A plebiscite was held in the territory on 13 January 1935.

With Adolf Hitler anxious for the propaganda advantages of the return of the Saar to Germany, Joseph Goebbels designed a concerted campaign to sway voters. The support of the local Catholic authorities for a return also helped, as did concerns about Bolshevism, against which Hitler was seen as a bulwark.[9] With a voter participation of 98%, the result of the plebiscite was that the overwhelming majority, 90.8%, voted to re-join the German Reich, with only 8.8% wanting to retain the status quo, primarily as they did not wish to be ruled by Nazis. A third option of joining France received 0.4% of the vote.

Following the vote, Hitler announced that Germany "had no further territorial demands to make of France".[9]

Many opponents of Nazism who had taken refuge in the territory and former politicians and office holders of the Saar who had collaborated with the occupation were imprisoned.

When re-incorporation was considered complete, the governor's title was changed again to Reichskommissar für das Saarland, "Reich Commissioner for the Saarland", on 17 June 1936. As the new Gau was extended to the Rhine, including the historic Palatinate, the region's name was changed again on 8 April 1940 to Saarpfalz, "Saar-Palatinate".

After the Battle of France, the re-annexed territory of the CdZ-Gebiet Lothringen was incorporated in the Reichsgau. The region's name was finalized on 11 March 1941 as Westmark, meaning "Western March" or "Western Boundary", with its governor styled as Reichsstatthalter in der Westmark, "Reich Governor in the Western March". On 28 September 1944 Josef Bürckel committed suicide, and he was succeeded by Willi Stöhr until 21 March 1945, when the region was conquered by troops of the United States Army, which handed over the occupation to French forces in July the same year.[10]

After World War II, a French protectorate was established within borders similar to those of the Territory. A referendum was held on 23 October 1955 which ended French rule and influence. On January 1, 1957, the Saarland re-joined Germany.